This proposal addresses fundamental issues of early conceptual development, language development, and the linkages between them. Children, like adults, are faced with an enormously rich environment. Each day, they encounter new objects and witness new events. This diversity would be overwhelming if each object and event were treated as unique. Therefore, an essential task of early childhood is to form categories that capture commonalities among objects and to learn words for these categories. Developmental research has documented that infants and toddlers appreciate many kinds of categories. Their cognitive achievements are concurrent with equally impressive gains in language acquisition. It is unlikely that their conceptual and linguistic advances are entirely independent. Indeed, recent developmental work reveals that particular types of words (e.g., nouns, adjectives) highlight particular types of conceptual relations (e.g., categories of objects, properties of objects). There are, however, two serious limitations in the existing work. First, because most of the existing literature is devoted primarily to preschool children who have already made significant linguistic advances, we have a very limited understanding of how they begin to build these important linkages early in development. Therefore, the proposed studies will chart carefully the emergence of these links in prelinguistic infants and in toddlers by examining the influence of language on their categorization abilities. Second, because the existing research has been based exclusively on English-speaking subjects, it is unclear whether they are universal to human development. The proposed studies will examine these linkages in young children learning languages other than English. They will build upon my preliminary with 2 other Indo-European languages (French , Spanish) and extend the investigation to include ASL, a non-Indo-European language that differs from the languages previously studied in syntax, morphology, and modality of transmission. The prediction is that some linkages (e.g., that between nouns and category relations) will emerge even before the child has made many linguistic advances, will be evident across human languages, and will initially be overextended to include words from other linguistic form classes (e.g., adjectives). In contrast, other links (e.g., that between adjectives and object properties) may emerge later, may rely upon an existing base of linguistic and conceptual knowledge, and may vary according to the specifics of the language being acquired. By combining developmental and cross-linguistic approaches, this research will 1) broaden considerably the empirical and theoretical foundations of existing research, 2) provide a window through which to view more clearly the origins of these powerful and precise linkages between early linguistic and conceptual development, and 3) enrich our understanding of early language and cognitive development.